The class of spirodilactones, as exemplified by 1,6-dioxospiro[4.4]-2,7-dione, has been known for a number of years. For example, see Pariza et al, Synthetic Communications, Vol. 13(3), pp. 243-254 (1983), and Cowsar et al, U.S. Pat. No. 4,064,086. Until recently, the corresponding classes of spirodilactams were unknown. Vanderbilt et al, "Biodegradable Polyamides Based on 4,4'-spirobibutyrolactone", Abstract, p. 521, ACS Meeting, Sept. 1988, Los Angeles, have described a polymeric system in which one monomeric unit has the 2,7-diazaspiro[4.4]nonane-3,8-dione ring system. No monomeric compounds are disclosed which incorporate this ring system. In a series of copending U.S. patent applications of which Serial No. 245,618, filed Sept. 16, 1988, is illustrative, monomeric compounds containing the 1,6-diazaspiro[4.4]nonane-2,7-dione are disclosed and claimed. By way of specific illustration, compounds such as 1,6-di(4-hydroxyphenyl)-1,6-diazaspiro[4.4]nonane-2,7-dione are prepared. This compound is useful as a precursor of polymeric materials, both thermoplastic and thermoset, which would contain the 1,6-diazapiro[4.4]nonane-2,7-dione ring system. Polymers containing the latter ring system, and presumably the ring system of Vanderbilt et al have many useful properties but in some applications demonstrate thermal oxidative instability and instability to water at elevated temperatures. Indeed, this is recognized by Vanderbilt et al who are seeking to find polymers for biomedical use which will biodegrade. For other applications, however, the thermal and water instability can be detrimental if polymers containing these spirodilactam ring systems are exposed to moisture or oxygen at elevated conditions.
Without wishing to be bound by any particular theory, whatever instability is observed is likely due to the presence within the molecule of active methylene hydrogen atoms which are alpha or adjacent to a carbonyl group. Any such difficulties of water or oxygen instability at elevated temperatures can be overcome by the substitution of the active methylene hydrogens with alkyl groups or other substituents. For example, there is disclosed in Ser. No. 245,618, filed Sept. 16, 1988, the production of compounds containing a 3,3,8,8-tetramethyl-1,6-diazspiro[4.4]nonane-2,7-dione ring system. Such ring substituted spirodilactams demonstrate greater thermal oxidative and hydrolytic stability at elevated temperatures. It would be of advantage, however, to provide a spirodilactam ring system which is free of active methylene carbon atoms and therefore demonstrates greater stability towards oxygen and moisture at elevated temperature.